VDSL sync and power cuts

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hashbrown

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Topic # 138855 19-Jan-2014 15:50

Anyone else notice that after an area wide power cut their sync rate goes up significantly? Makes sense as most peoples modems would be off so SNR would be low until they had all powered up.

Would be interesting to get a modem on a UPS and resync in the middle of a power cut then see what difference it made and then if the rate was sustainable. My experience is that the line stays up and stable albeit with a jump in HEC errors.

For reference my "normal" DS is around 35Mbit/s but after the last two power cuts, jumped to 44 and 39Mbit/s.

coffeebaron

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Reply # 969680 19-Jan-2014 15:57

Yep, happened to me recently. Higher sync lasted about 1 week, then re synced back to usual.

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Jase2985

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Reply # 969717 19-Jan-2014 18:12

maybe because you went to a different DLM upon re-sync?

coffeebaron

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Reply # 969753 19-Jan-2014 21:41

Jase2985: maybe because you went to a different DLM upon re-sync?

Most likely yes, as my error rate would have gone up. My line was sitting on 4dB noise margin!

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Coil

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Reply # 969840 20-Jan-2014 09:04

coffeebaron:
Jase2985: maybe because you went to a different DLM upon re-sync?

Most likely yes, as my error rate would have gone up. My line was sitting on 4dB noise margin!

Surprising it would make such a difference. I think there is a large amount of noise and interference in my area given my SL distance and synch rates.

sidefx

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Reply # 969859 20-Jan-2014 09:21

There have been a number of reports of this before.

I don't think it was DLM in the other cases (do you know what your interleaving\INP was before and after the power cut? :) ) - DLM changes usually seem occur at around 4am or a little after. They can occur at other times by it seems very infrequent.

My suggestion in the past was that maybe if your modem reconnects "quickly" before most other people, then there is less crosstalk, hence syncs higher - this might also be why the SNR Margin seems a bit lower afterwards. I think at the time someone in the know put the kibosh on this idea though...?

Still curious what might cause it though as a number of people including myself have observed it in the past when there has been a powercut. Maybe it's less interference from all electric items (in houses + streetlamps,etc)?

Coil

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Reply # 969878 20-Jan-2014 09:48

sidefx: Still curious what might cause it though as a number of people including myself have observed it in the past when there has been a powercut. Maybe it's less interference from all electric items (in houses + streetlamps,etc)?

Definitely the case, I would like to be able to do real world tests. See how big of a difference it is.

hashbrown

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Reply # 969881 20-Jan-2014 09:57

sidefx: There have been a number of reports of this before.

I don't think it was DLM in the other cases (do you know what your interleaving\INP was before and after the power cut? :) ) - DLM changes usually seem occur at around 4am or a little after. They can occur at other times by it seems very infrequent.

My suggestion in the past was that maybe if your modem reconnects "quickly" before most other people, then there is less crosstalk, hence syncs higher - this might also be why the SNR Margin seems a bit lower afterwards. I think at the time someone in the know put the kibosh on this idea though...?

Still curious what might cause it though as a number of people including myself have observed it in the past when there has been a powercut. Maybe it's less interference from all electric items (in houses + streetlamps,etc)?

I think @Jase2985 was referring to DLM triggering the resync that returns the line to "normal". After the initial training period changes are supposed to be weekly.

FWIW. I'm on day 11 of 39.4Mbit/s (Noise margin 9.6), so in theory I've survived at least one opportunity for DLM to resync my line. Have been on profile 1 the whole time. Can't remember how long I lasted at 44Mbit/s but it was at least a few days and only reset because I needed to disconnect the modem for some recabling.

Coil

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Reply # 969905 20-Jan-2014 10:44

hashbrown:I'm on day 11 of 39.4Mbit/s (Noise margin 9.6), so in theory I've survived at least one opportunity for DLM to resync my line. Have been on profile 1 the whole time. Can't remember how long I lasted at 44Mbit/s but it was at least a few days and only reset because I needed to disconnect the modem for some recabling.

What was throughput vs. sync? Increased ping times or lower?

hashbrown

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Reply # 969936 20-Jan-2014 11:20

TimA: What was throughput vs. sync? Increased ping times or lower?

I didn't keep any stats from when I was at 44Mbit, but I was able to get >40Mbit/s throughput. Wouldn't expect ping to go up unless the DLM profile changed.

coffeebaron

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Reply # 970017 20-Jan-2014 14:27

One person supports this post

sidefx: There have been a number of reports of this before.

I don't think it was DLM in the other cases (do you know what your interleaving\INP was before and after the power cut? :) ) - DLM changes usually seem occur at around 4am or a little after. They can occur at other times by it seems very infrequent.

My suggestion in the past was that maybe if your modem reconnects "quickly" before most other people, then there is less crosstalk, hence syncs higher - this might also be why the SNR Margin seems a bit lower afterwards. I think at the time someone in the know put the kibosh on this idea though...?

Still curious what might cause it though as a number of people including myself have observed it in the past when there has been a powercut. Maybe it's less interference from all electric items (in houses + streetlamps,etc)?

I have had the same with ADSL2. I have UPS, so restarted router during the power cut. Sync increased significantly. It then stayed connected at the higher speed, but obviously was more prone to errors. If I had manually rebooted at anytime, sync would have gone back to normal. Instead DLM finially caught up with me and said, hey your line sucks, let me change your profile! The good times ended :(

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plambrechtsen

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Reply # 970261 20-Jan-2014 20:11

If you are with Telecom I may be able to find out if any dlm shizzle had gone on.

coffeebaron

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Reply # 990604 19-Feb-2014 16:39

Before power cut:

After resetting during power cut on UPS

Image a little hard to read, but basically went from 14 Mbps to 21 Mbps downstream.

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